After a family-name formed by iñ the affix aṇ is added in the remaining senses.,
This debars अण् ॥ Thus from दक्ष we have Patronymic दाक्षि, from which दाक्षाः \the pupils of Dakshi\ ; प्लाक्षाः, माहकाः ॥ The final इ is elided before अण् by 6.4.148.
Why do we say 'denoting a family-name'? Observe सौतङ्गमिः, a word formed by इञ् of 4.2.80, not denoting a family, but having the four-fold sense of 4.2.68 - 4.2.70. The further derivative from this will be सौतङ्गमीयम् by छ 4.2.114.,